Commodity animals such as the chicken and cow offer the opportunity to produce recombinant pharmaceutical proteins through manipulation of the genes directing expression of proteins into their eggs and milk, respectively. The chicken was selected for these studies because of its high protein production capacity, and the availability of basic knowledge of the necessary (retroviral and oviduct) genetic systems. The ability to introduce specific genetic alterations in the somatic and germinal tissues of avian species is at hand, but the biological mechanisms involving the events from the moment of insertion of foreign genes into the chromosomes up to the final fate of their encoded product in vivo remain largely a mystery, since studies of foreign (non-viral) gene activity in avians are only now being successfully undertaken. It is proposed here to investigate the mechanisms of gene insertion and expression through the use of specially designed retroviral vectors employing classical and well-characterized genetic elements. The avian leukosis virus replicative element will be combined with a second transcriptional unit consisting of the steroid hormone-inducible chicken ovalbumin gene promoter and the cDNA sequences encoding pharmaceutical proteins (growth hormone, apolipoprotein A1). The insertion, expression, heritability, rearrangement, and pathology of the recombinant genes in mosaic (first generation) and transgenic (2nd and later generations) will be followed by well- known techniques of molecular biology. Successful completion of the experiments is expected to lead to the expression of Biomedical and pharmaceutical proteins into chickens' eggs. The development of new gene insertion technology and biological protein synthetic processes are logical, practical outcomes of the proposed work, in addition to acquisition of basic information about the control of gene expression in vivo.